1. Technical Field
The present invention relates to a light source device and a projector.
2. Related Art
Currently, a technology of incorporating a laser beam source in a projection type image display apparatus (projector) has been proposed, which display apparatus projects color light containing image information produced by a spatial light modulating device such as a liquid crystal device on a screen by using a projection system (for example, see JP-A-2007-33576).
A lighting device disclosed in JP-A-2007-33576 includes a light source device for emitting light and a diffraction optical element for equalizing illuminance distribution of entering light. The lighting device applies rectangular conversion to light emitted from the light source device by using the diffraction optical element and illuminates a predetermined illumination area. The projection type image display apparatus having this lighting device includes a light valve disposed opposed to the diffraction optical element, and illuminates the light valve by diffraction light produced by the diffraction optical element.
However, the related-art technology described above has the following problems.
When an illumination image obtained after rectangular conversion by the diffraction optical element is enlarged and projected via a projection lens, speckle patterns easily recognizable by human eyes are produced on the image. These speckles are generated by manufacture errors or design errors of the diffraction optical element. Since the image is expanded to about one hundred times larger image through the enlarged illumination by the projection lens at the time of display on the screen, the speckles are easily observed on the image.
A possible method for solving this problem is to provide a rotation type diffusing plate which rotates laser beam emitted from the light source, or a swing type diffusing plate which swings the laser beam in the vertical, horizontal, or other directions on the light source device. However, the rotation type diffusing plate requires a rotation driving system such as a motor, which increases the size of the device. Moreover, the rotation type and swing type diffusing plates which diffuse light emitted from the diffraction optical element have positional limitation in positioning these plates and decreases light utilization efficiency. Thus, according to the structure having the diffusing plate, reduction of the device size and space saving cannot be achieved.